1. Field of the Invention
The present invention relates to an image forming apparatus including a recording head that ejects liquid droplets and a method of correcting the shooting positions of the liquid droplets ejected from the recording head.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile machine, a copier, and a complex machine thereof, there is employed, e.g., a liquid ejection apparatus including a recording head composed of liquid ejection heads (liquid droplet ejection heads) that eject the liquid droplets of recording liquid (liquid) so as to perform image formation. In performing the image formation (that is used synonymously with recording, printing, and imaging), this liquid ejection apparatus causes recording liquid as liquid (hereinafter referred to as ink) to adhere to a sheet, while transferring a medium (hereinafter referred also to as the “sheet,” but it does not limit a material. Also, it is used synonymously with a medium to be recorded, a recording medium, a transfer member, a recording paper, etc.).
Note that the image forming apparatus refers to an apparatus that ejects liquid onto a medium such as a paper, a thread, a fiber, a fabric, leather, metal, a plastic, glass, wood, and a ceramic so as to perform the image formation. Furthermore, the “image formation” refers to forming on the medium not only meaningful images such as characters and graphics, but also meaningless images such as patterns. That is, the image forming apparatus refers also to a textile printing apparatus or an apparatus that forms a metal wiring. Furthermore, the “liquid” is not particularly limited so long as it is capable of performing the image formation.
When the image forming apparatus of such a liquid droplet ejection type causes a carriage, on which the recording heads that eject liquid droplets are mounted, to reciprocate so as to print the images of ruled lines bi-directionally, the deviation of the ruled lines is liable to occur in the forward and backward directions.
Generally, in an ink jet recording apparatus or the like, a test chart for adjusting the deviation of ruled lines is manually output so that users select and input an optimum value. Accordingly, ejection timing is adjusted based on the input results. However, viewing the test chart varies between users, and data are likely to be erroneously input because users are unaccustomed to the operations. As a result, an adjustment problem may be adversely incurred.
As one of the conventional image forming apparatuses of the liquid droplet ejection type, Patent Document 1 discloses an apparatus that prints test patterns on a recording medium or a transfer belt, scans the color data of the test patterns, and changes the driving conditions of heads based on the scanned results so as to correct density irregularities.
Patent Document 1: JP-A-4-39041
Furthermore, Patent Document 2 discloses an apparatus that forms the test patterns of mixed color dots made of cyan ink, magenta ink, and yellow ink in a prescribed area on a member for holding and transferring a print medium, scans the mixed color dots with a RGB sensor, and detects an ejection failure nozzle based on the scanned results.
Patent Document 2: Japanese Patent No. 3838251
Furthermore, Patent Document 3 discloses an apparatus that records on a part of a transfer belt the test patterns of either any of or the combination of a defective nozzle pattern for detecting a defective nozzle, a color shift pattern for detecting the color shift of ink, and a head position adjustment pattern for adjusting the position of recording heads; scans the test patterns with an image pickup unit such as a CCD; and makes a correction based on the scanned results.
Patent Document 3: JP-A-2005-342899
As the image forming apparatus of an electrophotographic type using toner, on the other hand, Patent Document 4 discloses an apparatus that forms toner images on a photoconductive drum and individually detects the density of the toner images having different characteristics with light emitting elements and light receiving elements wherein the light receiving elements serve to receive regular reflection light and diffused reflection light.
Patent Document 4: JP-A-5-249787
Furthermore, Patent Document 5 discloses an apparatus that detects a toner adhesion amount using the output obtained according to the results of a sensor capable of simultaneously detecting the regular reflection light and the diffused reflection light from toner images.
Patent Document 5: JP-A-2006-178396